This invention relates to a transportation system and specifically to an apparatus which controls the energization of a field circuit of a motive means moving and stopping a vehicle within the system.
D.C. motor control systems utilized for general motor applications have employed various speed regulating control loops in order to provide a full range of control. Some systems have held the field energization at a constant magnitude and variably controlled the armature voltage up to a predetermined base speed. Such systems have thereafter held the armature energization at a constant magnitude and variably controlled the field and particularly weakened the field in order to increase the speed above the predetermined base speed. Many of such systems have sensed the speed of the motor by using a tachometer for providing a speed proportional signal utilized in controlling the selective energization of the field in accordance with the varying speed characteristics provided by the motor output.
Other D.C. motor systems have sensed the controlled armature current supplied to the armature circuit for providing an armature current indicative signal for combination with a command signal to control the gating of uni-directional current to the field circuit. Some of these systems have been responsive to an excessive condition of the back EMF across the motor armature for discontinuing the current flow through the field coil thereby increasing the speed of the operating motor above the base speed.
Several known transportation systems such as battery powered vehicles have selectively controlled the conduction of direct current from the battery to the armature and field circuits of a D.C. motor and further operate to recharge the battery during certain sequences of the operation. One known system has controlled the operation of thyristors to selectively conduct the direct current from a battery to a D.C. motor field circuit in response to the sensed speed of the vehicle, the current flowing in the armature circuit, the commanded or desired field current and the actual field current supplied to the D.C. motor. One system as shown in U.S. Pat. No. 3,735,220 employs a first summing circuit responding to a minimum predetermined field current command signal, a speed signal and a sensed armature current signal for providing an output to a second summing circuit connected to receive a second field current command signal and a field current indicative signal with the second summing circuit interconnected to a third summing circuit which, in turn, is coupled to receive a predetermined braking current command signal, an armature current signal and a speed responsive signal so that the field current is controlled with an output to the controlled thyristors from the second summing circuit.